In the manufacture of some types of rigid pin-populated printed wiring boards, as many as 10,000 terminal pins are inserted into apertures of each of the boards. The boards are referred to as backplanes and typically measure eight inches by twenty-two inches on their sides. Typically, the spacing between adjacent apertures on each backplane is extremely small. For example, the spacing between apertures on one backplane is 0.125 inch. Moreover, each terminal pin typically has a square cross section of, for example 0.025 inch except in those areas where the pin is formed with (1) lateral ears having a push shoulder and (2) an aperture-engaging portion intermediate the ends thereof. The pin is relatively slender and typically measures one and one-half inches in length.
Each of the pins have slender shank portions which extend from opposite sides of the backplane. After the pins have been assembled with the backplane, the backplane is mounted in a frame where external wiring is wire wrapped to the pins on one side of the backplane commonly referred to as the wiring side. Other printed wiring boards, referred to as circuit packs, have electronic components electrically and mechanically secured thereto and have connectors secured to one end thereof. The connectors of these boards ultimately are inserted over selected ones of the pins extending from the other side of the backplane commonly referred to as the component side.
During the insertion of the pins into the apertures of the backplane and during subsequent handling of the pin-populated backplane, some of the pins may be bent undesirably. For example, the most severely bent pins may deviate from an axial centerline by 0.050 inch in any direction.
Since the component side of the pins are destined for insertion into a connector, and the pins on the wiring side may be wired by an automatic wiring facility, it is important that the pins be axially straight and perpendicular to the plane of the backplane within an acceptable tolerance. Otherwise, a slightly bent pin on the component side, for example, could be misaligned with its mating aperture in the connector. As the connector is moved into place, the bent pin would engage the face of the connector and would be bent further towards the surface of the backplane thereby failing to provide the required electrical connection. Such bent pins are very difficult to repair after they have been assembled and wired. More often, bent pins wear on mating connector surfaces, thus, degrading the electrical connection.
Since the pins are located on a grid spacing of 0.125 inch, and since the pins have a square cross section of 0.025 inch, the facing portions of adjacent pins are 0.100 inch apart. Consequently, it is most difficult to provide a facility for straightening pins which are so closely arranged. For example, a straightening facility typically is positionable over the tip of the pin to be straightened and is then moved in a selected motion whereby the walls of the opening engage and move the pin close to the centerline of the opening. To accomplish this straightening operation, a pin-receiving opening of the facility must be slightly larger in cross section than the cross section of the pin. Further, to insure that a bent pin will enter the pin-receiving opening, the mouth of the opening should be formed with a tapered or conical lead-in portion of sufficient dimension to receive any pin having a deviation as severe as 0.050 inch. Thus, the conical lead-in portion of the opening would require additional space in the cross section direction. In addition, the facility must have some bulk around the pin-receiving opening to provide for the opening and the conical lead-in portion. Thus, it is apparent that, with the close spacing between adjacent pins, it is most difficult to provide a sturdy facility which can accomplish the straightening of the pin.
Still another problem encountered in straightening the pins is due to warpage of the backplane after the pins have been inserted into the backplane. Such warpage is due to the pin density and the interfacial relationship between the apertures and the pins. Consequently, while any pin may be perpendicular with the backplane, if the backplane is warped, the tip of the pin would appear to be bent. This would provide an indication that the pin requires straightening even though the pin is perpendicular with the portion of the backplane surrounding the aperture into which the pin is mounted.
As noted above, as many as 10,000 pins are typically inserted into apertures of a single backplane. In a typical manufacturing operation, many pin-populated backplanes are assembled within relatively short periods of time. Since each pin must be straightened on both sides of the backplane, efficiency dictates that pluralities of pins be straightened simultaneously. However, when such mass pin straightening is considered, the above-mentioned problems resulting from the closeness of adjacent pins and warpage of the backplane pose serious difficulties.
Statistical studies have shown that processing each pin through two straightening wiggles provides tighter tolerance control of pin tip location. Such control will usually bring the pin tip within an acceptable tolerance of .+-.0.009 inch from true axial centerline.
In one prior system which provides facility for limited mass straightening of pins, a single bar has two rows of pin-receiving apertures formed in one surface thereof and is referred to herein after as the double-row bar. The pin-populated backplane is mounted on a table below the double-row bar. The double-row bar is lowered to position the tip ends of two adjacent rows of a plurality of rows of the pins into the pin-receiving apertures of the bar. Thereafter, the double-row bar is reciprocated, or wiggled, in the plane of the rows of pins which is referred to as the "X" direction. As the double-row bar is wiggled, the pins engage laterally spaced walls of the apertures whereby each of the pins is generally aligned in the "X" direction. The table is then reciprocated, or wiggled, in a plane referred to as the "Y" direction which is perpendicular to the plane of the "X" direction movement whereby the same pins are generally aligned in the "Y" direction. Thus, by this action, each of the pins in the two rows could be generally aligned with the centerline of the respective pin-receiving aperture. The double-row bar is then retracted and the table is indexed to locate the next two rows of pins directly beneath the two rows of apertures of the double-row bar. The double-row bar is then lowered and a straightening operation conducted as described above. This process continues until all pins are straightened. This type of system performs the straightening operation as described providing the grid spacing of the pins in the backplane is sufficiently spaced to avoid engagement by the double-row bar with previously straightened pins during the wiggle motion in the "Y" direction.
A prior system of this type is commercially available from Ambrit, Inc. of Wilmington, Massachusetts, as their Model No. 218.
In order to provide for the straightening of pins located on a grid spacing of 0.125 inch, a single bar having one row of apertures which is referred to hereinafter as the single-row bar, was utilized as described hereinabove. The width of the single-row bar measures about 0.125 inch. Thus, when the single-row bar is positioned over a single row of pins, the sides of the bar are located 0.050 inch from the pins of the immediately adjacent rows. A conical lead-in portion of each aperture of the single-row bar has a mouth diameter of 0.120 inch to insure that drastically bent pins are inserted into the pin-receiving aperture. The "X" and "Y" wiggle motion is the same as described above with respect to the double-row bar. In order to provide sufficient straightening effect in the "Y" direction, the table is wiggled to provide a 0.100 inch movement on each side of the centerline of the row of pins within the apertures of the single-row bar. Since the pins of the adjacent rows are only 0.050 inch from the side of the single-row bar, the adjacent pins are bent away from the pins located within the bar.
In order to compensate for this effect, a first row of pins located within the single-row bar are initially and properly straightened in the "X" direction. Thereafter, the table is wiggled, as noted above, in the "Y" direction. However, the pins of the first row are purposely not fully straightened in the "Y" direction but are leaning slightly in the "Y" direction toward the adjacent or second row of pins which is the next row of pins to be straightened. The single-row bar is then retracted and positioned over the second row of pins which are then straightened properly in the "X" direction. Thereafter, the bar is wiggled in the "Y" direction between the first and a third row of pins.
As noted above, the pins of the first row have been straightened in the "X" direction but are leaning slightly in the "Y" direction toward the second row of pins, the tip ends of which are now located within the apertures of the single-row bar. As the single-row bar is wiggled in the "Y" direction, one side of the bar engages the slightly bent pins of the first row and bends the pins in the "Y" direction so that the pins are now leaning away from the second row of pins. As the single-row bar moves in the wiggle motion toward the third row of pins and away from the first row of pins, the pins of the first row now tend to return to the initial position of leaning toward the second row of pins but only spring to a generally straightened position. After the bar has completed its wiggle motion in the "Y" direction, the pins of the second row are leaning slightly in the "Y" direction toward the third row of pins. In this way, the pins of the first row are generally straight but the pins of the second row are leaning in the "Y" direction toward the pins of the third row.
The single-row bar is then retracted and positioned over the tip ends of the pins of the third row and the pins are straightened in the "X" direction. The bar is wiggled in the "Y" direction whereby the pins of the second row are straightened in the "Y" direction in the same manner previously described with respect to the pins of the first row.
This pattern of operation is continued whereby the table is indexed in the "Y" direction to position successive rows of pins beneath the single-row bar. The single-row bar is then lowered over the tips of the pins and wiggled to straighten the pins in the "X" direction. The bar is then wiggled in the "Y" direction to effectively straighten the pins of the immediately trailing row in the "Y" direction while leaning the row of pins positioned within the bar toward the immediately forward row of pins. Ultimately, all pins of the backplane are thereby straightened in the "X" and "Y" directions.
The above-described single-row bar straightens one row of pins at a time. In addition, due to the closeness of the adjacent rows of pins, the single-row system must depend on the side of the bar for straightening the pins in the "Y" direction. Further, a limited number of pins is straightened using the single-row bar.